The present invention relates to a method according to the precharacterizing part of claim 1 as well as to an apparatus to use this method.
In hearing devices, batteries are almost exclusively used as electrical energy sources. Thereby, exactly adjustable and stable supply voltages are required in order for a hearing device to fulfil its task error-free. Furthermore, several values for supply voltages which deviate from the battery voltage are often necessary and which values, sometimes, must be larger than the battery voltage itself.
To generate a higher supply voltage than the source voltage, i.e. the battery voltage, the use of a so-called voltage multiplication circuit is known. Nevertheless, such a circuit comprises the disadvantage that only integer multiple of the source voltage can be generated. Thereby, the conditions demanded by hearing devices cannot be fulfilled. In addition, it is of great importance for power line independent devices to sparingly use the energy which is available. Furthermore, the expenditure for the circuit should be kept low. In addition, the changes of the battery voltage depending on influences of age or of the outside have to be observed, since just these changes are the cause of low voltage precision, especially when using voltage multiplication circuits for a voltage increase.
The object of the present invention is therefore to provide a method to generate constant and stable supply voltages.
This will be reached by the measures given in the characterizing part of claim 1. Further embodiments of the present invention as well as an apparatus are given in further claims.
The present invention comprises the following advantages:
Starting from a battery voltage which may change on grounds of age or in dependence on the load, a stable supply voltage is generated the value of which may also be greater than the battery voltage. If need be, the present invention may also be used to generate several supply voltages of different values. The present invention can especially be used for the integration on a micro chip which is especially important when using it for a hearing device.